Pressure-sensitive polyurethane adhesives

ABSTRACT

Pressure-sensitive polyurethane adhesives having the combined properties of high peel adhesion, quick stick, shear strength, and resistance to hydrocarbon solvents comprise the crosslinked polyurethane reaction product of the in situ reaction of polyhydroxyl terminated polyethers and polyethers with polyisocyanates to provide a product having a molecular weight between crosslinks of about 6,000 to about 40,000 and a urethane group concentration of about 0.7 to 1.3 per 1,000 gms of polymer, and trackifier comprising the reaction product of cyclic terpene alcohols and aromatic isocyanates. The adhesive is coated as a layer on a backing of paper or polymeric film and wound in a roll. A silicone treated release liner may be adhered to the adhesive layer. The adhesive may also be coated as a transfer film on a release liner.

United States Patent [1 1 Tushaus 1 Oct. 23, 1973 [75] Inventor: LeonardA. Tushaus, St. Paul, Minn.

[73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul,Minn.

[22] Filed: Nov. 20, 1972 [21] Appl. No.: 307,873

Related U.S. Application Data [62] Division of Ser. No. 119,838, March1, 1971, Pat.

[52] U.S. Cl 206/59 C [51] Int. Cl B65d 85/67 [58] Field of Search206/59 C [56] References Cited UNITED STATES PATENTS 3,035,690 5/1962Frohbach 206/59 C X, 3,491,877 1/1970 Viker et al 206/59 C PrimaryExaminerLeonard Summer Attorney-Temple Clayton [57] ABSTRACTPressure-sensitive polyurethane adhesives having the combined propertiesof high peel adhesion, quick stick, shear strength, and resistance tohydrocarbon solvents comprise the crosslinked polyurethane reactionproduct of the in situ reaction of polyhydroxyl terminated polyethersand polyethers with polyisocyanates to provide a product having amolecular weight between crosslinks of about 6,000 to about 40,000 and aurethane group concentration of about 0.7 to 1.3 per 1,000 gms ofpolymer, and trackifier comprising the reaction product of cyclicterpene alcohols and aromatic isocyanates. The adhesive is coated as alayer on a backing of paper or polymeric film and wound in a roll. Asilicone treated release liner may be adhered to the adhesive layer. Theadhesive may also be coated as a transfer film on a release liner.

4 Claims, No Drawings PRESSURE-SENSITIVE POLYURETHANE ADHESIVES Thisapplication is a division of copending U.S. Pat. application Ser. No.119,838, filed Mar. 1, 1971, now U.S. Pat. No. 3,718,712.

FIELD OF THE INVENTION This invention relates to pressure-sensitivepolyurethane adhesives and adhesive tapes.

Pressure-sensitive adhesives and adhesive tapes having excellentproperties and adhesion to numerous substrates have historically beenprovided by means of rubber-resin compositions and more recently bymeans of acrylate polymer compositions. Despite their desirableproperties, these adhesives have not combined solvent resistance withhigh peel adhesion, quick stick, and shear strength. For example, theseadhesives have not been suitable for use in environments where they areexposed to organic solvents because those adhesives having adequate peeladhesion, quick stick, and shear strength are not resistant to thesolvent, while adhesives having adequate solvent resistance are limitedin their applications because they do not have adequate peel adhesion,quick stick, and shear strength.

Certain polyurethane pressure-sensitive adhesives having some resistanceto solvents are known in the art. For example, urethane polymerstackified with various non-reactive tackifiers are disclosed in U.S.Pat. No. 3,246,049 and 3,437,622. However, these adhesives requirerelatively long cure times and generally are deficient in one or moreadhesion properties.

Other pressure-sensitive polyurethane adhesives are disclosed in BritishPat. No. 1,113,925; U.S. Pat. No. 2,983,693; and U.S. Pat. No.3,515,773. These adhesives do not utilize tackifiers and have not beenfound satisfactory for use as pressure-sensitive adhesives because oftheir low peel adhesion and quick stick.

SUMMARY OF THE INVENTION The invention provides pressure-sensitivepolyurethane adhesives and adhesive tapes combining the properties ofhigh peel adhesion, quick stick, and shear strength with resistance tohydrocarbon solvents. This combination of properties makes theseadhesives particularly adapted for use in environments exposed tohydrocarbon solvents. Adhesive properties can be tailored at will byvarying the reaction components to provide a desired balance ofproperties, such as increased water sensitivity, peel adhesion or quickstick.

In accordance with the invention, pressure-sensitive polyurethaneadhesives having the combined properties of high peel adhesion, quickstick, shear strength and resistance to hydrocarbon solvents comprisethe crosslinked polyurethane reaction product of the in situ reaction ofpolyhydroxyl terminated polyethers and polyesters with polyisocyanatesto provide a product having a molecular weight between cross-links ofabout 6,000 to about 40,000, preferably about 6,500 to about 20,000, anda urethane group concentration of about 0.7 to 1.3 per 1,000 gms ofpolymer, and tackifier comprising the reaction product of cyclic terpenealcohols and aromatic isocyanates.

DETAILED DESCRIPTION OF THE INVENTION The desirable properties of thepressure-sensitive adhesives of the invention are obtained by combiningthe described tackifier with a cross-linked polyurethane reactionproduct. The urethane reaction product, to provide the desiredproperties, must have a molecular weight between crosslinks of about6,000 to about 40,000 and a urethane group concentration of about 0.7 toabout 1.3 per 1,000 gms of polymer. The molecular weight betweencrosslinks is the average molecular weight of chains connecting twocrosslink sites. This value is two-thirds of the molecular weight percrosslink which is defined as the unit weight of polymer divided by thenumber of crosslink junctions in the unit weight of polymer. Forexample, if a polyurethane were prepared from 1,000 grams of reactants,using a stoiehiometric ratio of reactants, and 0.25 mole of triol in the1,000 grams, all other reactants being difunctional, the hypotheticalmolecular weight per crosslink would be 1,000/0.25 or 4,000. Theurethane content is defined as the equivalents of urethane per 1,000gms. of polymer.

The polyurethane polymers having the above properties may be obtained byseveral methods. One is to prepare a hydroxyl or isocyanate terminatedpolyurethane prepolymer and crosslink it with triisocyanate or triol toobtain the final polymer, the triol being utilized to crosslinkdiisocyanate prepolymers and the triisocyanate being utilized withpolyol prepolymers. Useful prepolymers are obtained by reacting at leastone polyhydroxy terminated polyether or polyester having a molecularweight of about 400 to about 4,000 preferably about 1,000 to about 3,000with at least one diisocyanate to provide a urethane prepolymer havingeither hydroxyl or isocyanate termination. As previously mentioned, atriol or triisocyanate is then used for crosslinking to prepare thefinal polymer.

The polyols used to prepare the useful polyurethane prepolymers includepolyhydroxy ethers (substituted or unsubstituted polyalkylene etherglycols or polyhydroxy polyalkylene ethers), ethylene oxide or propyleneoxide adducts of polyols, polyhydroxy polyesters, polycaprolactones,etc. The diisocyanates used to prepare the useful prepolymers arearomatic diisocyanates such as toluene diisocyanate, ethylbenzenediisocyanate, xylene diisocyanate, methyldiphenyl methane diisocyanate,dimethyldiphenylmethane diisocyanate, dichloroxylene diisocyanate,dimethoxybiphenyl diisocyanate, and others.

The polyol and diisocyanate reaction to provide useful prepolymers canprovide either hydroxyl or isocyanate terminated prepolymers. That is,either polyisocyanate or polyol is used in excess such that the finalprepolymer contains either isocyanate or hydroxyl polyfunctionality.Hydroxyl terminated prepolymers are preferred because they areconsiderably more stable than isocyanate terminated prepolymers and maybe readily stored for future use without fear of spontaneouscrosslinking. Various methods of preparing these prepolymers are knownin the art, preferred techniques and prepolymers being shown in theexamples appended hereto.

The cross-linking agents utilized with the above described prepolymersto provide the urethane polymers used in making the pressure-sensitiveadhesives of the invention are of two general types. When an isocyanateterminated prepolymer is utilized, the curing agent is a polymeric triolhaving a molecular weight between about 1,000 and 5,000, preferablybetween about 1,500 and about 3,000. Such triols are commonly obtainedby extending a triol such as glycerine, trimethylol propane,1,2,6-hexane triol, etc. with propylene oxide, ethylene oxide or both.When a hydroxyl terminated polyurethane prepolymer is utilized, thecrosslinking agent is a triisocyanate such as that obtained by thereaction of trimethylol propane and toluene diisocyanate in an NCO tohydroxyl ratio of 2:1, triphenylmethane triisocynate, or2,4,4'-triisocyanato diphenylether.

Another technique or method of obtaining the polyurethane polymers usedto make the adhesive of the invention is to react high molecular weightpolyols with diisocyanate to provide a polymer which is then crosslinkedwith either triisocyanate or triol to obtain the polyurethane polymerused to prepare the pressuresensitive adhesives of the invention. Thisprocedure can be reversed, if desired, and high molecular weightdiisocyanates reacted with diols.

The tackifiers utilized in the compositions of the invention comprisethe reaction product of cyclic terpene alcohols and aromaticisocyanates. Typical starting materials for such reaction productsinclude the aromatic diisocyanates and the tricyclic diterpene alcoholdescribed in U.S. Pat. No. 2,867,644 as a mixture of 14 to 23 percentabietyl alcohol, 36 to 39 percent dihydro abietyl alcohol, and 39 to 50percent of tetrahydro abietyl alcohol. Other suitable cyclic terpenealcohols for preparing the tackifiers are such as a-terpineol, geraniol,citronellol, abietyl alcohol, dihydroabietyl alcohol, tetrahydroabietylalcohol, dehydroabietyl alcohol, Z-hydroxy-methyl-S-norborene,6,6-dimethyl bicyclo (3,1,1)-2-heptene-2-ethanol, B-terpineol, gammaterpineol, dihydro-a-terpineol, menthol, neomenthol, fenchyl alcohol,borneol, isoborneol.

If desired, some polyhydric alcohols may be incorporated in thetackifier together with the cyclic terpene alcohol. Preferably, at leastabout 50 percent by weight of the alcohols should be terpene alcohol.Examples of polyhydric alcohols that may be used in preparing thetackifier are such as trimethylol propane, trimethylolethane,pentaerythritol, sorbitol, mannitol, 1,2,6- hexanetriol, diethyleneglycol, dipropylene glycol, tripropylene glycol, dipentaerthritol,glycerol, glycerinepropylene oxide adducts, 1,2,6-hexanetriol-propyleneoxide adducts, ethylene glycol, propylene glycol, tetramethylene glycol,tris (dipropylene glycol) phosphite, etc.

The isocyanates useful for reaction with cyclic terpene alcohols forpreparing the tackifiers utilized inthe invention are such as toluenediisocyanate, triphenylmethane triisocyanate (Mondur TM), methylene bis(4-phenylisocyanate), hexamethylene diisocyanate, 3,-3-dimethoxy-4,4'-diphenylene diisocyanate, 4-methoxy-l,3-phenylenediisocyanate, poly(phenylmethylene) triisocyanate (PAPI),1,5-naphthalene diisocyanate, the reaction product of toluenediisocyanate with trimethylol propane at an NCO/OH ratio of 2:1 (MondurCB), phenyl isocyanate, p-tolyl isocyanate, m-chlorophenyl isocyanate,naphthyl isocyanate, etc.

The ratio of isocyanate to hydroxyl'equivalents in preparing thetackifier is about 0.5 to about 1.25, preferably about 0.9 to about 1.1.Thus, the tackifier may be either isocyanate or alcohol terminated inwhich case the tackifier is reactive with the polyurethane polymer inpreparing an adhesive. If desired, the tackifier may be reacted withmonohydric alcohols or amines to provide a non-reactive tackifier.

These tackifiers have been found effective with the previously describedpolyurethanes to provide excellent pressure-sensitive adhesives.However, these tackifiers have not been found effective with naturalrubber or styrene-butadiene rubbers to provide pressuresensitiveadhesives. Use of these tackifiers with polyurethanes other than thosedescribed herein have not been found to be satisfactorypressure-sensitive adhe- SlVeS.

The finished adhesive to be effective as a pressuresensitive adhesiveand contain the aforementioned balance of properties should containabout 20 to about 75, preferably about 35 to about parts by weight oftackifier per parts by weight of urethane polymer. The ratios ofisocyanate: hydroxyl groups in the composition of reactants making upthe final adhesive composition should be approximately stoichiometric(i.e., NCO:Ol-l ratio of 1.0 i 0.2) regardless of the source of theisocyanate or hydroxyl.

In practice, the adhesive components are combined in a solvent, coatedon a desired substrate, surface, or backing and cured in situ in adrying oven. The reaction is preferably accelerated and catalyzed by useof about 0.1 gm per equivalent of isocyanate of a catalyst such as lead2-ethylhexoate, stannous 2-ethylhexoate, dibutyl tin dilaurate, or othercommon urethane catalyst. When a catalyst is used, the curing time isapproximately 10 minutes or less at -300 F. If desired, antioxidantssuch as those disclosed in U.S. Pat. No. 3,494,880 may be incorporatedin the adhesive composition. The solvents utilized in coating theadhesive composition are those whichdissolve the polyurethane polymerand are such as aromatic hydrocarbons, ketones, ethers, esters, oraliphatic or cycloaliphatic organic solvents. Specific examples aretoluene, benzene xylene,'methyl ethyl ketone, ethyl acetate, cellosolveacetate, dimethyl ether of ethylene glycol, heptane, cyclohexane,dioxane, etc. The non-volatile content utilized is dependent upon theviscosity and coating weight desired and is that which provides asolution viscosity that is readily coatable upon a tape backing byconventional tape coating equipment. Polyurethane adhesives may beutilized in high solids solutions thereby minimizing pollution problemsand efiecting a cost saving.

The aforedescribed adhesive compositions may be coated upon numeroustypes of self-supporting backings to provide adhesive tapes. Suchbackings may be polymeric films such as polyethylene terephthalate,polyvinyl chloride, cellulose acetate, etc. impregnated cellulosicmaterials may be utilized to prepare paper backed masking tapes. It isalso possible to prepare transfer films by coating the adhesivecomposition of the invention on release liners such as silicone coatedpapers.

The following examples in which all parts are by weight unless otherwisenoted, illustrate preparation of the polymers, tackifiers, and adhesivesof this invention, without limiting the scope thereof.

DESCRIPTION OF THE PREFERRED I EMBODIMENTS EXAMPLES l-l2 These examplesillustrate preparation of the tackifier resins utilized in the pressuresensitive adhesives of the invention. Resin softening points weredetermined in accordance with ASTM E28-58T.

Example 1 1 gm. equivalent weight of a mixture of terpene alcoholscomprising about 14 to 23 percent abietyl alcohol, 36 to 39 percentdihydro abietyl alcohol, and 39 to 50 percent tetrahydro abietyl alcohol(commercially available from Hercules, Inc. under the trade designationAbitol) was placed in a three-neck round-bottom reaction flask fittedwith mechanical stirrer, thermometer, nitrogen inlet tube, and droppingfunnel. The terpene alcohol was heated to 100 C and one equivalent oftoluene diisocyanate (TDl) slowly added from the dropping funnel. Thereaction temperature was allowed to increase to l70180 C and the mixturestirred for about 3 hours. Then, the resin was poured into a flat panand allowed to harden. The resin was found to have a softening point ofabout 95 C.

Example 2 0.8 equivalent of the terpene alcohol used in Example 1 and1.0 equivalent of toluene diisocyanate were reacted by the procedure ofExample 1. The product had a softening point of 91 C.

Example 3 2.0 equivalents of the terpene alcohol used in Example l and1.0 equivalent of toluene diisocyanate were reacted by the procedureused in Example 1. A resin was obtained having a softening point of 51C.

Example 4 Example 5 0.8 equivalent of the terpene alcohol used inExample 1 and 0.3 equivalent of the triisocyanate reaction product fromone equivalent of trimethylol propane and two equivalents of toluenediisocyanate (commercially available from Mobay Chemical Co. under thetrade designation Mondur CB) were placed together in a three-neckedround-bottom flask like the one used in Example 1. The temperature wasraised to 100 C, with stirring, and 0.5 equivalent of toluenediisocyanate added dropwise. After 3 hours the temperature had risen to190 C. at which time the resin was poured out. It has a softening pointof 102 C.

Example 6 0.4 equivalent of the terpene alcohol used in Example l and0.4 equivalent of polypropylene glycol having a molecular weight of 400were placed in the threenecked round-bottom flask used'in Example 1. Thetemperature was allowed to rise to 100 C. and 0.8 equivalent of toluenediisocyanate added dropwise in a nitrogen atmosphere. The temperaturewas raised to 160 C., maintained for three hours, and the resin pouredout. The product had a softening point of 75 C.

Example 7 0.6 equivalent of the terpene alcohol used in Example l and0.2 equivalent of polyethylene glycol having a molecular weight of 400were reacted with 0.8 equivalent of toluene diisocyanate as described inExample 6. The product had a softening point of 78 C.

Example 8 0.3 equivalent of the terpene alcohol used in Example l and0.02 equivalent of polycaprolactone having a molecular weight of 2,000were reacted with 0.32 equivalent of toluene diisocyanate as describedin Example 6. A resinous product was obtained having a softening pointof 73 C.

Example 9 0.9 equivalent of the terpene alcohol used in Exam ple 1 and1.5 equivalents of trimethylol propane were heated together to 80 C. ina three-necked roundbottom flask equipped as in Example 1. 2.5equivalents of toluene diisocyanate were added dropwise. The reactiontemperature was allowed to rise to 190 C. and the product poured into aflat pan. The softening point was C.

Example 10 1 equivalent of 2-hydroxymethyl-S-norbornene and 1.0equivalent of toleuene diisocyanate were reacted as in Example 1. Aresinous product having a softening point of 69 C. was obtained.

Example 11 A sample of tackifier comprising the reaction product oftoluene diisocyanate and the terpene alcohols used in Example 1 (Abitol)and having a slight stoichiometric excess of the diisocyanate(commercially available from Schenectady Chemicals, Inc. under the tradedesignation lsoterp 95") was reacted at 150 F. for about 2 hours withsufficient polypropylene glycol having a molecular weight of 2,700, inthe presence of lead octoate catalyst, to react the excess isocyanate.Sufficient toluene was utilized to provide a 50 percent solids solution.Upon completion of the reaction, the resinous product was poured into apan and dried.

Example 12 A sample of the tackifier used in Example 11 (Isoterp 95) wasreacted in a 50 percent solids toluene solution with sufficient dibutylamine to react the excess isocyanate in the resin. Following reaction,the resin was poured into apan and dried.

Examples 13-25 These examples illustrate preparation and evaluation ofpressure-sensitive polyurethane adhesives utilizing the tackifiersprepared in Examples l-l2.

A hydroxyl terminated polyurethane prepolymer was prepared by reacting419 parts by weight of a polypropylene oxide-ethylene oxide blockcopolymer having 10 percent polyoxyethylene groups and a hydroxyl valueof 44.5 (commercially available from the Wyandotte Chemical Companyunder the trade designation Pluronic L-8l) with parts of apre-prepolymer comprising poly(tetramethylene glycol) and toluenediisocyanate and having an amine equivalent weight of 650 (commerciallyavailable from E. l. DuPont de Nemours & Co., Inc. under the tradedesignation Adiprene L-167). The reaction was catalyzed with 15 parts byweight of a percent lead octoate solution. Sufficient toluene was addedto provide a 70 percent solids polymer solution. The solution viscosityafter standing at room temperature for 24 hours was 9,600 cps.

Adhesives were prepared as shown in Table I by combining (1) 40.32 partsby weight of the above polyurethane prepolymer with (2) 2.0 parts byweight of crosslinking agent having an isocyanate content of percent andcomprising a triisocyanate made from 1 equivalent of trimethylol propaneand 2 equivalents of toluene diisocyanate (commercially available fromthe Mobay Chemical Company under the trade designation Mondur CB), and(3) tackifier from Examples 1-12 as shown in Table I, the tackifierbeing dissolved in toluene to form a 50 percent solution by weight.

Each of the adhesive compositions was coated on biaxially oriented 1.5mil polyethylene terephthalate film and cured at 250 F. for 10 minutes.Tapes were prepared by cutting the coated adhesive sheets into ,2 inchwide strips and the peel and shear strength determined in accordancewith Pressure Sensitive Tape Council tests 1 and 7. The shear strengthwas obtained using a k inch X A inch bond of adhesive on a stainlesssteel panel and a load of 1,000 gms.

Quick stick of each adhesive was determined by allowing about a 1 inchlength of a 10 inch closed loop of 1 inch wide tape to come in contactwith a clean 4 inch X 8 inch X A inch glass plate, no pressure beingused other than the weight of the tape. If the adhesive will support theweight of the glass plate, the adhesive is considered to have excellentquick stick. Each of the polyurethane adhesives of Examples 13-25supported the glass plate, whereas a commercial solvent-resistantacrylate adhesive failed to support the glass plate.

Quick stick of each adhesive was also evaluated by means of PSTC-6modified to utilize a 1 inch diameter (80 gm) ball. Solvent-resistantacrylate adhesives permit the ball to roll a minimum of about 18 inches.The polyurethane adhesives of Examples 13-25 only permittedthe ball toroll about 3 inches, this being about the same distance obtained withrubber-resin adhesives.

A sample of each of the tapes of Examples 13-25 was adhered to a steelpanel and immersed in an agitated heptane bath for 24 hours at roomtemperature. Tapes made with rubber-resin and acrylate adhesives weresimilarly bonded to steel panels and immersed in heptane. In eachinstance, the rubber resin adhesive was dissolved so the tape fell fromthe steel plate. The acrylate adhesive was softened and peeled easilyfrom the steel plate. The polyurethane adhesives were only slightlysoftened at the edges of the tape backing, the peel adhesion being firmand steady.

TABLE I Coneentra- Peel Shear tion (parts per Adhesion Adhesion ExampleTackifier 100 parts of (oz./in.) (minutes) polymer) 13 Example 1 50 2610,000+ 14 Example 2 40 5O 15 Example 3 40 38 127 16 Example 4 50 2410,000+ 17 Example 5 50 40 10,000+ 18 Example 6 50 26 10,000+ 19 Example7 40 30 4,703 20 Example 8 50 30 10,000+

21 Example 9 50 64 10,000+ 22 Example 10 50 24 23 Example 11 50 26 24Example 12 50 51 538 25 (Control) 0 2 Example 26 This Exampleillustrates preparation of a pressuresensitive polyurethane adhesiveutilizing an isocyanate terminated polyurethane prepolymer and a polyolcuring agent. 40.00 parts of a polyurethane preprepolymer having anequivalent weight of 1,000 and comprising poly(tetramethylene glycol)end-capped with toluene diisocyanate (commercially available from E. I.DuPont de Nemours & Co., Inc. under the trade designation Adiprene L-)was thoroughly mixed with 1 10.4 parts of a 50 percent toluene solutionof tackifier resin prepared according to Example 1 to provide a solutioncontaining about 65 parts by weight of tackifier per 100 parts by weightof urethane polymer. To this was added 27.36 parts of a polypropyleneoxide-ethylene oxide block copolymer having 10 percent polyoxyethylenegroups and a hydroxyl value of 44.5 (commercially available fromWyandotte Chemical Company under the trade designation Pluronic L-8l),71.58 parts of a trio] comprising the addition product of trimethylolpropane and propylene oxide and having a hydroxyl number of 63,(commercially available from Wyandotte Chemical Company under the tradedesignation Pluracol TP2540 20.64 parts of toluene and 2.0 parts of a 5percent solution of lead octoate in xylene. After thorough mixing, thesolution was coated onto 1.5 mil polyester film and cured atapproximately 200 F for 10 minutes. A firm, tacky adhesive was obtained.

The tape of this examples was subjected to a solvent resistant test(Federal specification L-T-lOOa) by applying a one inch wide strip oftape to a smooth, aluminum panel and immersing the panel for- 24 hoursin a mixture of solvents comprising 60 percent by volume of isooctane, 5percent of benzene, 20 percent of toluene and 15 percent of xylene. Peeladhesion was measured on a tensile-testing machine (Instron) with thestressing jaw moving at a speed of 12 inches per minute. For comparison,two commercial adhesive tapes were tested under the same conditions onehaving a natural rubber base and the other a phenolformaldehyde resincured SBR-Neoprene base. Results are reported in Table II. Thepolyurethane adhesive lifted the glass plate and stopped the steel ballin 3% inches when subjected to the tests previously described.

TABLE II SOLVENT RESISTANCE TEST Peel Adhesion (oz. per inch) AdhesiveThis Example illustrates preparation of a pressuresensitive polyurethaneadhesive which is sensitive to water but still resistant to hydrocarbonsolvents. The following materials were thoroughly mixed together:

1 12.0 parts of poly(ethylene glycol) of 1,000 molecular weight(commercially available from the Union Carbide Corporation under thetrade designation Carbowax 1,000).

380.0 parts of polypropylene oxide-ethylene oxide block copolymer having10 percent polyoxyethylene groups and a hydroxyl value of 44.5(commercially available from the Wyandotte Chemical Company under thetrade designation Pluronic L-8 l 39.0 parts of tolylene diisocyanate212.3 parts of ethyl acetate 15.2 parts of a 5 percent solution of leadoctoate An exothermic reaction occurred which was allowed to continuewithout the application of external heat. After 24 hours the viscositywas 19,280 centipoises.

To 23.7 parts of the above prepolymer was added 1.0 part of atriisocyanate prepared from trimethylolpropane and toluene diisocyanate(commercially available from the Mobay Chemical Company under the tradedesignation Mondur CB-60) 18.0 parts of a 50 percent toluene solution ofthe tackifier prepared in Example 1 was also added. After mixing, thesolution was coated on a silicone coated release liner and cured at 250F, a tacky film being formed. The adhesive was then transferred to labelstock paper and labels applied to glass bottles. The pressure-sensitivelabels could be removed quite readily from the glass by brief contactwith water. In the absence of water, these labels could not be removedwithout delaminating the label. The adhesive possessed good quick stickand peel adhesion.

Examples 28-29 Example 28 The following materials were thoroughly mixedtogether: Part A 350.00 parts of polypropylene glycol having a molecularweight of about 2,000 and a hydroxy number of about 56.

70.70 parts of the addition product of trimethylolpropane and propyleneoxide having a molecular weight of about 1,535 and a hydroxyl number ofabout 110. 12.25 parts of a 5 percent toluene solution of lead octoate0.7 part 2,6-di-t-butyl-4-methylphenol anti-oxidant 0.7 part2,4-dimethyl-6-t-butylphenol anti-oxidant Part B 278.00 parts of a 50percent solution of the tackifier of Example 1 in heptane 42.63 parts oftoluene diisocyanate Part A (216.3 parts) and Part B (160 parts) weremixed together just prior to coating on a vinyl film. Both sides of thevinyl were coated and the adhesive cured by passing the web through athree zone oven having temperatures of 150 F., 200 F., and 200 F. Totalcure time was 10 minutes. The product exhibited a desirable limited bondbuild-up to natural rubber and possessed good quick stick, shearstrength, and peel adhesion.

Example 29 The following were mixed together:

69.0 parts of isocyanate terminated urethane polymer comprisingpoly(tetramethylene glycol) and toluene diisocyanate and having an amineequivalent weight of 650.

90.0 parts of polypropylene glycol having a molecular weight of about2,000 and a hydroxyl number of about 56.

8.8 parts of the addition product of trimethylolpropane and propyleneoxide having a molecular weight of about 1,535 and a hydroxyl number ofabout 110.

To 10 parts of this master batch was added 8 parts of a 50 percenttoluene solution of the tackifier of Example 12 and 0.3 part of a 5percent toluene solution of lead octoate. The solution was coated onpolyester and cured for 10 minutes at 200 F. An adhesive with good quickstick, peel adhesion, and shear strength was obtained.

Example 30 This Example illustrates use of Nopol in preparing atackifying resin and use of the resin in polyurethane adhesives. Oneequivalent of 6,6-dimethyl bicyclo (3,1,1)-2-heptene-2-ethanol(commercially available from the Glidden-Durkee Co. under the tradedesignation Nopol) was heated to 50 C. and 1 equivalent of toluenediisocyanate added dropwise with the temperature being allowed to riseto about 180 C. The resin was then poured into a pan and found to have asoftening point of about 50 C. A hydroxyl-terminated prepolymer wasprepared by reacting 170.1 parts by weight of a polypropyleneoxide-ethylene block copolymer having 10 percent polyoxy ethylene groupsand a hydroxyl value of 41.5 (commercially available from the WyandotteChemical Company under the trade designation Pluronic L-81) with 63.4parts of a poly(tetramethyle ne glycol)-toluene diisocyanate adducthaving an amine equivalent weight of 660 (commercially available fromDuPont under the trade designation Adiprene L-167). The reaction wascatalyzed with 5.7 parts by weight of a 5 percent lead octoate solution.Additional toluene, 94.4 parts by weight, brought the solution topercent solids. The solution viscosity after standing at roomtemperature for 24 hours was 36,250 cps.

An adhesive was prepared by combining (1) 55.6 parts by weight of theabove hydroxyl-terminated prepolymer with (2) 2.0 parts by weight ofcross-linking agent having an isocyanate content of about 10 percent andcomprising a triisocyanate made from 1 equivalent of trimethylol propaneand 2 equivalents of toluene diisocyanate (commercially available fromthe Mobay Chemical Company under the trade designation Mondur CB) and(3) 40.0 parts by weight of a 50 percent solution of the tackifierprepared above in toluene. Similar adhesives were made with the sameweight ratios but with the tackifier of Example 1 and Example 5. Tapeswere prepared as described in Examples 13-25 and evaluated as thereindescribed. Peel and shear adhesion data are given in Table III. Each ofthe tackified adhesives lifted the glass plate, stopped the large steelball within 3 inches, and were resistant to heptane solvent.

TABLE III Peel Shear Tackifier Adhesion Adhesion Tackifier Conc.(phr)(oz/inch) (minutes) None (control) 6 From Example 1 50 53 10,000+ FromExample 30 50 54 85 From Example 5 50 44 10,000+

What is claimed is:

1. An adhesive tape comprising a thin, flexible, selfsupporting backinghaving adhered to at least one major surface thereof a polyurethanepressure-sensitive adhesive comprising a crosslinked polyurethane and atackifier for said crosslinked polyurethane,

said crosslinked polyurethane being a cured reaction product ofcomponents comprising a polyol and a polyisocyanate, said crosslinkedpolyurethane having a molecular weight between crosslinks of 6,000 to40,000 and a urethane group concentration of 0.7 to 1.3 urethane groupsper 1,000 grams of said crosslinked polyurethane,

said tackifier comprising a resin which is the reaction product of thecomponents comprising a cyclic terpene alcohol and an aromaticpolyisocyanate, said resin having been combined with said crosslinkedpolyurethane prior to the completion of the curing of said crosslinkedpolyurethane,

said tape being wound directly upon itself in overlapping convolutionsin roll form and capable of being unwound therefrom without delaminatingor offsetting. 2. Tape of claim 1 wherein said backing is biaxiallyoriented polyethylene terephthalate film.

3. Tape of claim 1 wherein said backing is polyvinyl chloride film.

4. An adhesive tape comprising a thin, flexible sheet of paper havingadhered to one major surface thereof a pressure-sensitive polyurethaneadhesive and having a thin, flexible, silicone treated release lineradhered to said adhesive, said adhesive comprising a crosslinkedpolyurethane and a tackifier for said crosslinked polyurethane,

said crosslinked polyurethane being a cured reaction product ofcomponents comprising a polyol and a polyisocyanate, said crosslinkedpolyurethane having a molecular weight between crosslinks of 6,000 to40,000 and a urethane group concentration of 0.7 to 1.3 urethane groupsper 1,000 grams of said crosslinked polyurethane,

said tackifier comprising a resin which is the reaction product of thecomponents comprising a cyclic terpene alcohol and an aromaticpolyisocyanate, said resin having been combined with said crosslinkedpolyurethane prior to the completion of the curing of said crosslinkedpolyurethane,

said tape being wound directly upon itself in overlapping convolutionsin roll-form and capable of being unwound therefrom without delaminatingor offsetting.

2. Tape of claim 1 wherein said backing is biaxially orientedpolyethylene terephthalate film.
 3. Tape of claim 1 wherein said backingis polyvinyl chloride film.
 4. An adhesive tape comprising a thin,flexible sheet of paper having adhered to one major surface thereof apressure-sensitive polyurethane adhesive and having a thin, flexible,silicone treated release liner adhered to said adhesive, said adhesivecomprising a crosslinked polyurethane and a tackifier for saidcrosslinked polyurethane, said crosslinked polyurethane being a curedreaction product of components comprising a polyol and a polyisocyanate,said crosslinked polyurethane having a molecular weight betweencrosslinks of 6,000 to 40,000 and a urethane group concentration of 0.7to 1.3 urethane groups per 1,000 grams of said crosslinked polyurethane,said tackifier comprising a resin which is the reaction product of thecomponents comprising a cyclic terpene alcohol and an aromaticpolyisocyanate, said resin having been combined with said crosslinkedpolyurethane prior to the completion of the curing of said crosslinkedpolyurethane, said tape being wound directly upon itself in overlappingconvolutions in roll form and capable of being unwound therefrom withoutdelaminating or offsetting.